Relations between BlackBerry and T-Mobile have turned frosty after a promotion last week saw T-Mobile BlackBerry users offered a cheap iPhone.

Relations between BlackBerry and T-Mobile have turned frosty after a promotion last week saw T-Mobile BlackBerry users offered a cheap iPhone.

The email promotion offered some T-Mobile customers an iPhone 5s for $500, a saving of $150 on the retail price.

Apple iPhone 5S

BlackBerry has seen its user base contract in recent years as consumers were won over by iPhones and Android devices, so many current BlackBerry users are either those on company-issued devices or the very loyal. And the T-Mobile promotion didn't sit well with the BlackBerry loyalists.

On Tuesday, BlackBerry CEO John Chen took to the company's blog and said BlackBerry was "outraged" by the "clearly inappropriate and ill-conceived marketing promotion."

"As we were never told of their plans in advance, I can only guess that T-Mobile thought its 'great offer for BlackBerry customers' would be well received. T-Mobile could not have been more wrong," said Chen.

He went on to say the relationship between the companies was "once productive and profitable for both BlackBerry and T-Mobile" and that he hopes the companies can "find a way forward that allows us to serve our shared customers once again."

BlackBerry declined to comment further on the status of its relationship with T-Mobile.